Why is s.3 and s.4 of HRA significant in terms of challenging parliamentary sovereignty?

s.3 in effect imposes a purposive approach to interpreting legislation - that it should be read in accordance with convention rights. Historically, the courts were to interpret legislation with a literal approach as to do otherwise would risk inferring a will contrary to that of parliament. This challenges parliamentary sovereignty as its intention must be balanced alongside the ECHR.
s.4 allows for Declarations of Incompatibility - the Court is able to declare legislation passed by Parliament incompatible with the ECHR with the view that it be repealed. This challenges the tenet of parliamentary sovereignty that parliament has supreme lawmaking powers.